For many years, cinemas and other similar venues have used audio loudspeakers to distribute sound throughout a large area. In cinemas, for example, it is common to use a group of several loudspeakers, where each of the loudspeakers in the group may be placed at some position along the side and rear walls of the room. In this arrangement, each individual loudspeaker may project sound to only a portion of the audience nearest to the loudspeaker and the combined sound from all of the loudspeakers is used to cover the entire audience area.
While this arrangement is useful for distributing sound uniformly across a large audience area, recent developments in cinema sound require that each loudspeaker independently be able to provide sound to the entire audience. For example, cinema sound now often employs localized sources of sound where individual sound elements from a movie or other media content may be projected by as few as one loudspeaker of a group of loudspeakers. The ability to project individual sound elements from particular loudspeakers of a group enables sound designers to create immersive sound environments which increase the sense of realism for the audience.
In order for the entire audience to hear sound clearly from individual loudspeakers, it is desirable that each loudspeaker be able to disperse sound in a wide horizontal pattern covering the audience area. In addition, limited dispersion of sound in a vertical direction is often desirable so that sound energy is not wasted in areas where audience members typically are not located (e.g., directly above and below a loudspeaker) and so that listeners nearest the loudspeaker are not subjected to dramatically higher sound levels than listeners at the furthest distance across the room.
One way in which the directivity of sound generated by loudspeakers may be controlled is with the use of rectangular shaped horns. A horn generally is a device that may be acoustically coupled to a sound source, such as a loudspeaker, and used to more efficiently project and guide sound generated by the source. Sound generated by a source travels through a “throat” section of the horn having an outwardly expanding cross sectional area toward an outlet, or horn “mouth.” Upon exiting the horn mouth, the sound exhibits a dispersion pattern that is approximately controlled by the shape of the horn. For example, a rectangular shaped horn is defined by side walls, which determine an amount of horizontal dispersion of sound emanating from the horn, and top and bottom walls, which determine an amount of vertical dispersion of sound emanating from the horn.
As indicated above, in some instances it is desirable for a loudspeaker to widely disperse sound in one direction (e.g., in a horizontal pattern) while limiting dispersion of sound in another (e.g., in a vertical pattern). One way to control the dispersion of sound in one direction relative to another is using a rectangular shaped horn having a narrow exit in one direction, also referred to as a slot exit. For example, a horn with slot exit may taper out in the vertical direction, but have a narrow and constant width in the horizontal direction for the entire length of the horn. A horn with such a slot exit generally causes sound to emanate with relatively limited vertical coverage pattern and, due to the narrow horizontal width of the slot exit causing the exiting sound to diffract, with a wide horizontal coverage pattern.
Although a horn with a slot exit generally is able to control the dispersion of sound in one direction relative to another, at sufficiently high frequencies, sound transmitted through a slot exit horn may nevertheless become more directional in both directions. For example, as the frequency of sound increases and its wavelength approaches the width of the slot exit, the diffracting effect of the slot exit is minimized. Narrower slot exits may be used in an attempt to increase diffraction of higher frequency sounds; however, there are limits to the sound energy levels that may be transmitted through narrow slots without degrading the sound quality.
The approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section. Similarly, issues identified with respect to one or more approaches should not assume to have been recognized in any prior art on the basis of this section, unless otherwise indicated.